The present invention relates to a knocking determination apparatus for an internal combustion engine having an intake injector for injecting fuel into an intake system and an in-cylinder injector for injecting fuel into a combustion chamber.
An internal combustion engine having two different types of injectors for separately injecting fuel into an intake system, such as an air intake port, and a combustion chamber is known in the prior art (refer to Japanese Laid-Open Patent Publication 7-103048).
This type of internal combustion engine improves fuel consumption and ensures appropriate engine output by switching fuel injection modes with the two types of injectors in accordance with the engine operating conditions.
A typical internal combustion engine performs knocking control, which includes a knocking determination process for determining whether or not knocking has occurred and a process for adjusting ignition timing or the like in accordance with the result of the determination. The knocking determination process determines whether or not knocking has occurred according to a detection signal from a knock sensor that detects vibration of the cylinder block, particularly, vibration of cylinders after ignition.
In a conventional internal combustion engine, fuel injection into a combustion chamber is more apt to cause uneven fuel distribution in the combustion chamber compared to fuel injection into an intake system. When an air-fuel mixture containing unevenly distributed fuel is ignited, part of the air-fuel mixture where the fuel concentration is high burns rapidly. This increases the combustion rate of the air-fuel mixture. Thus, knocking occurs in different manners depending on whether fuel is injected by the in-cylinder injector or intake injector. For example, the timing when knocking occurs and the level of engine vibration caused by the knocking differs between in-cylinder injector fuel injection and intake injector fuel injection. Therefore, an internal combustion engine having such two types of injectors often exhibits low reliability in the determination of knocking.